A slide fastener generally comprises a pair of stringer tapes along confronting edges of which are mounted rows of coupling heads or teeth which interdigitate upon movement of a slider along these rows.
The tapes and the respective rows of coupling heads form stringers which can be provided at the opposite ends with stop members (endstop members) preventing withdrawal of a slider, means for coupling the two tapes or slide-fastener halves together in the case of a nonseparable slide fastener, or male and female formations enabling the coupling and decoupling of the stringer halves in the case of a separable slide fastener.
The tapes are generally incorporated, e.g. by stitching, in opposite sides of an article having an opening which can be closed by the slide fastener. The slide-fastener art has advanced rapidly in recent years both with respect to techniques with the fabrication of the stringers and with respect to improvements in the mechanical and esthetic properties thereof.
For example, woven support tapes which have hitherto been provided with the coupling heads by clamping, molding or rows of stitching, have increasingly been provided with the heads directly during the tape-weaving operation utilizing conventional or only slightly modified tape looms to allow the coupling heads to be mounted on the edges of the tape as the tape is woven.
In recent years, moreover, individually mounted coupling heads have tended to be replaced by continuous coupling elements composed of a synthetic resin monofilament and of coil or meander configuration. The individual coupling heads can be formed by deformation, e.g. molding, bending or kinking the monofilament at spaced-apart locations, to so shape the head that it has lateral protrusions which can engage behind the heads of the opposing coupling element when the two are interdigitated, i.e. when the heads of one coupling element are fitted into the interstices or head spaces of the opposing coupling element.
The heads have shanks which reach toward the respective tapes and can be connected to the shanks of adjoining heads by connecting members or bights. Each head and the associated pair of shanks will be referred to hereinafter as a coupling member and, because coils of the type described have a generally dentate configuration, the coupling heads of the coupling members may be referred to as "teeth."
With respect to woven support tapes, reference will be made to the ground weave which, of course, is intended to mean the woven fabric consisting of weft yarns and warp yarns to which the coupling element is secured. The coupling element itself is the continuous monofilament member provided with the succession of coupling members as defined above, therealong.
A ground weft is, therefore, a weft yarn structure of the ground weave. A "double weft" or "double weft insertion" is a weft of a single yarn having two passes received in the same warp pockets or shed in traversing the tape.
Reference will also be made herein to "warp pockets" for the sake of convenience. In a conventional weaving operation, the warp is shedded, i.e. certain of the warp yarns are lifted while others are lowered from the plane of the tape and, between the lifted and lowered warps forming the shed, a weft is inserted. This is referred to as a weft insertion.
When the heddles are next activated, other warp yarns are lifted and lowered, respectively, to form another shed in which a weft insertion is placed. As a consequence, the warps which pass over and under a particular weft insertion form "pockets" in which the weft can be said to have been inserted.
Reference may also be had to German Open Application (Offenlegungsschrift) DE-OS No. 22 19 907 and the corresponding U.S. Pat. No. 3,880,203 of the present applicant, issued Apr. 29, 1975, in which a stringer is described having a stringer tape composed of the warp yarns and double wefts formed from a continuous ground weft yarn. The coupling element is here woven into the tape or is secured to the tape by weaving. In this case, the two shanks of each coupling member can also form a double weft which is secured to the ground weave by warp yarns at least in part.
The aforementioned copending applications and their corresponding German applications P No. 29 41 067.1 and P No. 30 07 276.5 also make it clear that each coupling head, overhanging an edge of the respective support tape, can have a pair of shanks reaching inwardly from this edge, these shanks being superposed, i.e. so oriented that one shank lies above the other so that the two shanks together form the equivalent of a double weft constituting a single weft insert in respective pockets of a binding warp, i.e. warp yarns which are interwoven with the double-weft yarns of the ground weave and also serve to anchor the coupling element to the support tape.
To simplify the description of the prior art, as far as it concerns the present application, and to distinguish sharply the point at which the invention begins, it should be noted that it is known to provide a slide fastener stringer with a woven support tape and a synthetic resin monofilament coupling element woven into this tape, the tape comprising ground warp yarns and successive weft inserts in the form of double wefts of a continuous ground weft yarn, the coupling element having coupling members each of whose shanks form a synthetic resin monofilament double weft disposed such that one shank lies directly above the other, i.e. the shanks have a common projection in the slide-fastener plane or projections which are substantially superimposed.
These coupling members are interconnected in the continuous coupling element by arcuate bights and the shanks are engaged by binding weft yarns and thereby united with the tape. Furthermore, the double-weft insertions of the ground weft yarn, in the region between the coupling members and the double-weft insertions of the ground weft yarn elsewhere in the tape fabric and beneath the coupling members are received in respective warp pockets, these warp pockets including warp pockets directly underlying the bights.
Slide-fastener stringers of this type can be formed by needle weft insertion tape looms at high speeds using needles to insert the double weft insertions of the ground weft yarn on the one hand and the double weft insertions of the monofilament on the other.
In the above mentioned application Ser. No. 195,000, corresponding to German application P No. 29 41 067.1, there is claimed a slide-fastener stringer of the latter type in which the binding warp yarns are in a pattern offset from one another by two weft insertions (two-pick stagger), each passing over (overshooting) a pair of coupling members in succession, overshooting the next (third) coupling member and passing under (undershooting) the next (fourth) coupling member in the repetition pattern. Furthermore, each binding warp yarn, between the overshot pair of coupling members and the next (third) coupling member in the repetition pattern is, in turn, overshot by double-weft insertions of the ground weft yarn while the binding warp yarns overshoot the double weft insertions of the ground weft between the individually overshot (third) member and the undershot (fourth) member of the repetition.
While this arrangement has been found to be highly successful in affording high production rates and an effective stringer, the structure described is inherently associated with a problem described below.
Since the binding warp yarns do not form bridges with the ground weft yarns, the double-weft insertions of the ground weft yarns on the one hand and the monofilament double-weft insertions on the other hand lie at different levels transverse to the slide-fastener plane in the two slide-fastener halves.
Furthermore, the binding warp yarns extend to the region of the bights, i.e. practically overlie the bent portions which interconnect the coupling members.
It has been found that, when the two slide-fastener heads are fabricated as a continuous band or web by high speed needle-insertion looms of the aforedescribed type, whereby the stringers are separated from this band subsequently, it is necessary to "gap" the coupling elements at spaced locations along the length of the continuous band or web.
Such gapping is required in the semifinished product to enable a slider to be drawn onto the interconnected coupling elements of each section of the band intended to form a respective spring. The stringer length can then be cut apart from one another at the region formed by the gapping action and, if desired, endstop members or the like can be applied.
The gapping is effected by stamping or cutting away all or part of one or more coupling members in the region in which coupling is desired. When the bights of the otherwise continuous monofilament coupling elements are severed, cut away or otherwise destroyed by the gapping procedure, the gapping members thus freed from the continuity of the strand can pull out, the binding warp yarns can unravel and the connection of the coupling element to the tape can be destroyed.
This danger is especially pronounced when the bindings of the yards lie against the bight or extend over the arcuate portions thereof.
As a result, the continuous band produced by the aforedescribed method and with the structure set forth in application Ser. No. 195,000 has been treated as a nongappable band, i.e. a preliminary gapping in the region of the gapping members is avoided and the stringers are severed from the band in an operation which retains the coupling elements in a stable condition as the slider is applied for in a procedure whereby endstop members are formed on the stringers thus severed from the band.